The project is specifically designed to obtain biochemical data on the lenses of a cohort of patients undergoing surgery for age-related cataract and to correlate these data with those already acquired for the same cohort during the Italian-American case-control study (IACS1) and during the Italian-American natural history study (IACS2) on age-related cataract. Data collected in the course of the above mentioned epidemiological studies include a) cataract classification (clinical and photographic) and complete ophthalmological evaluation, b) medical and nutritional interview, c) biochemical data on plasma and on several RBC enzymes, d) identification of risk factors, and e) evaluation of the progression rate. By April 1, 1989 a certain number of these patients will have already had surgery but it is expected that the majority of them will need cataract removal within the next two or three years. Biochemical analysis will be performed on lens capsule epithelium preparations obtained after extracapsular extraction or, on a much smaller sample of lenses, on the whole lens after intracapsular extraction. Factors under investigation include epithelial enzymes, evaluation of thiamine and riboflavin status, sugar alcohols, water and ion content. By accomplishing these objectives, the study has the potential of filling the gap presently existing in our knowledge and concerning the absence of information on how biochemical changes in the lens relate to individual risk factors, nutritional status, progression rate of the disease.